The present invention relates generally to a method and apparatus for compressing measurement data correlative to machine status, and in particular, to a method and apparatus for compressing machine vibration data to allow significant compression of the original data for storage and transmission wherein the compressed data can be retrieved and reconstructed to provide a complete continuous waveshape history of machine performance.
Machinery monitoring systems have been permanently installed in, inter alia, today""s large process plants, power generation stations and pipelines in an attempt to provide machinery protection by continuously monitoring the behavior and performance characteristics of machinery at a multiplicity of points and possibly acquiring data from these points simultaneously. More recently, the trend has been to enhance the monitoring systems by directly interfacing computers to the systems for periodically collecting data from these systems for historical trend, machinery diagnostics and predictive maintenance purposes. However, these current systems use methods which only retain a small history of machine performance at best.
For example, current systems periodically collect, store, display and print machinery data in a variety of formats using a variety of schemes. One such scheme is to continuously sample and store data at a high sample rate to obtain data with relatively high data time resolution, and as storage space fills, to replace the stored data with a new data set. This scheme does not automatically store the historical information necessary to analyze one or more problems, may not represent a long enough period of time to represent the on-set of one or more problems and does not readily identify the occurrence of one or more problems.
Another scheme is to intermittently capture data xe2x80x9csnapshotsxe2x80x9d of the machine performance. A small set of xe2x80x9csnapshotsxe2x80x9d are maintained in memory and saved in the event of a machine problem. However, the time represented by the xe2x80x9csnapshotsxe2x80x9d may not be adequate to represent historical machine performance or may not represent a continuous set of data with the machine fault occurring between data sets previously stored in memory.
A common scheme is to represent the machine performance with an overall magnitude, eliminating all of the details that are contained to generate the magnitude. Although the magnitude can be used for protection, it does little to identify the causes of the problem.
The disadvantage of these schemes is they either consume too much memory, may not provide a rapid method to identify when one or more problems commence and to describe its progress or may lose the ability to diagnose one or more problems after the fact by either destroying the data with replacement information, or by taking data samples with the data of interest falling between the samples.
Therefore, if one were to continuously capture the machine data using current techniques, the memory requirements of such data storage can be enormous considering that the data is preferably collected over a period of months or years. In addition, long transmission times are required for transmitting large quantities of continuous machine data to a remote data base for permanent storage and with enough detail and history to perform fault analysis and diagnosis.
In addition, with current systems it is a challenge to capture and store infrequently occurring machine anomalies and to ensure that these anomalous events get managed using past learning experiences and procedures according to historical data. For example, the cause of and the procedures needed to deal with these machine anomalies may not be repetitive enough to stay within peoples"" memory. Further, to make matters worse, many anomalous events occur so infrequently that people who managed and learned from previous situations have either changed jobs or are not available by the time a similar anomalous event occurs again. These anomalous events can have a profound impact if not managed correctly. For example, improper management of one of these anomalous events may cause loss of life, loss of property, fugitive emissions and other undesirable consequences.
Therefore, what is needed is a system which, inter alia, allows machine data to be compressed and stored in a reduced form which represents a continuous set of data correlative to a continuous history of machine performance without allowing machine faults between data sets to go undetected and thus unrepresentable. In addition, a need exists for a system which reduces data volume sufficiently to allow transmission using commonly available transmission media. Furthermore, a need exists for a system which allows stored compressed data to be retrieved and reconstructed to provide a complete continuous waveshape history of machine performance. Moreover, a system is needed which provides continuous data acquisition for diagnostic and predictive maintenance purposes for maximizing the machine""s life while minimizing its cost and averting any catastrophic events when in operation.
U.S. Pat. No. 4,908,785 issued Mar. 13, 1990, to Cubbins, et al., teaches the use of a data compression method for telemetry of vibration data. The method achieves compression by filtering the incoming signal to extract a low frequency band. This low frequency band is sent to a multiplexed system without encryption or compression but can be sampled at a lower frequency since the upper frequency has been significantly reduced. The total range of frequencies is then divided, either by fractional octave filters, DFT or FFT to amplitude detect bands of frequencies and then the magnitude of the signals in this band or bands are extracted. These magnitudes are multiplexed with the lower frequency signals to give an overall or specific distribution of energy. Once processed, the low frequency data can be extracted but a waveshape can not be generated from the information present.
The present invention is distinguished over the known prior art in a multiplicity of ways. For one thing, the present invention provides a system for compressing, storing and transmitting raw dynamic machine data in a reduced form which can be retrieved and reconstructed into a continuous set of data correlative to a continuous waveshape history of machine performance without allowing machine faults between data sets to go undetected and thus unrepresentable. In addition, the present invention reduces data volume sufficiently to allow transmission using commonly available transmission media by, inter alia, retaining only significant data and by eliminating data created from noise sources. Furthermore, the present invention provides a system which continuously collects and stores information on machine performance to generate a historical data base which captures, inter alia, infrequently occurring machine anomalies and allows historical dynamic machine performance data to be retrieved and reconstructed including machine phase information. The system also allows a rule set to be generated from the historical data which is an accurate assessment of these anomalous events. The present invention further provides a system which allows access to the data base at any time so that past learned machine performance can be used. Moreover, the present invention provides a system which, inter alia, provides continuous life time data acquisition for diagnostic and predictive maintenance purposes for maximizing the machines life while minimizing its cost and averting any catastrophic events when in operation.
In one preferred form, the system of the present invention includes a computational means operatively coupled to a sampling means and to at least one machine, for example, to at least one bearing or measurement point to be monitored. The system is adapted to receive signals from a plurality of sensors operatively coupled to the machine. Preferably, the sampling means is operatively coupled to and receives data from at least one sensor sensing raw dynamic machine vibration signals correlative to machine status. Preferably, the computational means incorporates a timing pulse into commands given to the sampling means for synchronously sampling the raw dynamic machine vibration signals into discrete digital values. Alternatively, the computational means can issue commands to the sampling means for sampling the raw dynamic machine vibration signals into discrete digital values asynchronously with machine speed. These discrete digital values are transmitted to the computational means and are processed in sets according to the present invention.
The computational means performs a fast fourier transform analysis on a first data set of digital values to preferably transform the data into a series of spectral elements including both amplitude and phase information. The spectral elements are compared to a dominate criteria and those which pass this criteria are stored in a memory means along with a unique identifying tag. The identifying tag preferably tags each spectral element with an element number and a real time value identifying a time in history when the corresponding instantaneous value of the raw vibration signal was captured from the vibration sensor. The spectral elements of the first data set which have passed the dominate criteria can be transmitted to and stored in, for example, the host computer along with at least one unique identifying tag associating an element number and real-time value to each transmitted spectral element.
The computational means transforms a subsequent set of digital values into a subsequent series of spectral elements which are compared to the dominate criteria and those which pass are stored in the memory means and compared to the first set of spectral elements which have been previously stored in the memory means for determining any anomalous behavior between the two. Only those elements included in the subsequent series which are anomalous, because they differ by a comparison criteria from the first set of spectral elements are stored in the memory means. In addition, the anomalous spectral elements in the subsequent series can be are transmitted to and stored in the host computer along with at least one unique identifying tag associating an element number and a real-time value to each transmitted spectral element.
The computational means transforms each further subsequent set of digital values into further subsequent series of spectral elements which are each compared to the dominate criteria and those which pass are compared to the previous set of spectral elements which have been stored in the memory means for determining any anomalous behavior between subsequent sets. Only those elements included in each further subsequent series which are anomalous are stored in the memory means and can be transmitted to and stored in the host computer along with at least one unique identifying tag associating an element number and a real-time value to each transmitted spectral element. In addition, information regarding the sample rate of the raw vibration signals is stored in the memory means and transmitted to and stored in the host computer.
The data is preferably transmitted to and stored in the host computer as a spectral frequency element number, in phase and quadrature magnitudes and/or amplitude and phase elements and a real time reference. The spectral frequency is preferably related to shaft speed or time. After receipt of the data, the host computer can perform an inverse fourier transform to regenerate a continuous waveshape from the significant spectral content for any given time in history.
For example, the computer can recreate a continuous waveshape at any given time by using the anomalous spectral elements representing performance for that time. These are accessed by sequencing backwards through the stored spectral element sets to identify and use only those elements whose magnitudes are found to have significance at the desired point in time. These elements will have been identified to have a significant magnitude and/or phase prior to the desired point in time and will exist to a time later than the desired point. The combination of all elements which fit this existence criteria will be included to construct the waveshape. Thus, a continuous waveshape history of machine status at any given time may only require a few anomalous spectral elements to be stored for that given time. Therefore, the present invention provides a significant improvement in data compression, the consumption of memory to store this data and the time needed to transmit this data to a remote location.
The compression method of this invention is a lossy technique and thus, once the data is compressed the original signal cannot be recreated exactly. However, the compression technique of the present invention is highly effective because it only retains the significant content of the data and it preferable only stores the data if it has changed from previously stored data.
An object of the present invention is to provide a new, novel and useful apparatus and method for compressing measurement data correlative to machine status.
A further object of the present invention is to provide an apparatus and method as characterized above which collects measurement data at a predetermined mode and samples the data input over a number of input cycles and transforms the data using a fast fourier transform method.
Another further object of the present invention is to provide an apparatus and method as characterized above for compressing, storing and transmitting raw dynamic machine data in a reduced form.
Another further object of the present invention is to provide an apparatus and method as characterized above which reduces data volume sufficiently to allow transmission using commonly available transmission media by retaining only significant data.
Another further object of the present invention is to provide an apparatus and method as characterized above which reduces data volume by eliminating data created by noise sources in the system.
Another further object of the present invention is to provide an apparatus and method as characterized above which allows historical dynamic machine performance data to be retrieved and reconstructed including machine phase information.
Another further object of the present invention is to provide an apparatus and method as characterized above for providing a continuous set of data correlative to a continuous history of machine performance without allowing machine faults between data sets to go undetected and thus unrepresentable.
Another further object of the present invention is to provide an apparatus and method as characterized above which continuously collects and stores information on machine performance to generate a historical data base which captures, inter alia, infrequently occurring machine anomalies.
Another further object of the present invention is to provide an apparatus and method as characterized above which allows access to the data at any time so that past learned machine performance can be used.
Another further object of the present invention is to provide an apparatus and method as characterized above which provides continuous lifetime data acquisition for diagnostic and predictive maintenance purposes.
Viewed from a first vantage point, it is an object of the present invention to provide a signal processing method for processing machinery signals correlative to machine status, the steps including: sensing signals correlative to machine status; converting said signals into digital values; storing a series of said digital values into packets; comparing a subsequent packet of said digital values with one said stored packet of said digital values; storing only said digital values included in said subsequent packet which are anomalous because they differ by a criteria from comparable digital values of said previously stored packet of said digital values; transmitting a signal correlative to said packet of digital values and to the subsequent packets including flagging anomalous data in said subsequent packets of digital values.
Viewed from a second vantage point, it is an object of the present invention to provide a machine vibration signal processing method, the steps including: sampling a vibration signal; subjecting said vibration signal to a transformation means for transforming said vibration signal into a series of spectral elements; comparing said series of spectral elements against a criteria for retention and storing in a memory means said spectral elements which pass said criteria; sampling a subsequent vibration signal; subjecting said subsequent vibration signal to said transformation means for transforming said subsequent vibration signal into a subsequent series of spectral elements; comparing said subsequent series of spectral elements to said criteria for retention and then comparing said subsequent series of spectral elements which have passed said criteria for retention with said previously stored series of spectral elements; storing in said memory means spectral elements of said subsequent series which have passed said criteria for retention and which differ from said spectral elements of said previous series by a pre-determined amount.
Viewed from a third vantage point, it is an object of the present invention to provide an apparatus for compressing data correlative to continuous machine vibrations signals, comprising, in combination: at least one sensor operatively coupled to a machine for sensing machine vibration in the form of continuous electrical signals; sampling means adapted to receive from said sensor continuous electrical signals and to converting into digital values said electrical signals; a control circuit commanding said sampling means to convert said electrical signals into digital values; means for uniquely tagging each digital value with each command by said control circuit including a real time value for identifying a time in history of when the corresponding instantaneous value of the continuous electrical signal was captured; means for storing in a memory means a periodicity of said digital values; means for comparing at least one said periodicity of said digital values with a subsequent periodicity of said digital values to determine anomalous digital values, and means for storing in said memory means said anomalous digital values of said subsequent periodicity of said digital values which have changed from said previous periodicity of said digital values.
Viewed from a fourth vantage point, it is an object of the present invention to provide a machine vibration signal processing method, the steps including: sampling continuous vibration signals from a machine; transforming said vibration signals into discrete digital values; storing at least one packet of digital values in a memory means and storing a marker in said memory means for identifying the position and the time of capture of each digital value; comparing a subsequent packet of digital values with at least one said packet of digital values; storing digital values of said subsequent packet of digital values which differ from at least one said packet of digital values and storing markers for identifying the position and time of capture of each differing value; comparing further subsequent packets of digital values with previously stored packets of digital values; storing digital values of said further subsequent packets of digital values which differ from said previously stored values and storing markers in said memory means identifying the position and time of capture of each differing value; reconstituting any packet of digital values into a continuous wave form from the values stored for said packet and from the values of previous packets which correspond to the missing values of said packet being reconstituted.
Viewed from a fifth vantage point, it is an object of the present invention to provide a signal compression method for storing historical data correlative to devolving machine status, the steps including: sensing signals correlative to machine status; sampling said signals; transforming said sampled signals into a series of spectral elements defining a first reading; determining dominate spectral components of a periodicity of said series of spectral elements based on a pre-determined criteria; storing said periodicity of dominate spectral components; determining dominate spectral components of a subsequent periodicity of said series of spectral elements based on said pre-determined criteria; comparing said subsequent periodicity of dominant spectral components with said previously stored periodicity of dominant spectral components to ascertain devolvement in respect of spectral components correlative to machine status; transmitting to and storing in a host computer said spectral components of said subsequent periodicity which change from said spectral components of said previously stored spectral components and when the changes occur; defaulting to resensing in the absence of devolvement; generating a continuous signal correlative to a continuous signal in which said subsequent periodicity of dominant spectral components was produced from by transforming said stored components of said subsequent periodicity and said stored components of said previous periodicity which fails to differ from said subsequent periodicity of dominant spectral components.
Viewed from a sixth vantage point, it is an object of the present invention to provide a method for compressing data from waveforms characterizing machine vibration, the steps including: successively producing a series of samples representing generally instantaneous values of a series of waveforms at time-spaced intervals; transforming a first period of said samples of a first waveform included in said series of waveforms into a first series of spectral elements storing only those elements in said first series of spectral elements which are significant based on a predetermined criteria; transforming said series of samples of each subsequent waveform included in said series of waveforms into a subsequent series of spectral elements; successively storing only those elements in each said subsequent series which have changed since the last stored elements in said series of spectral elements.
Viewed from a seventh vantage point, it is an object of the present invention to provide a method for compressing measurement data correlative to machine status, the steps including: sensing machine data correlative to machine status; sampling said data; transforming said sampled data into spectral elements; comparing said spectral elements to a user definable criteria for retention; storing in a memory means those spectral elements which have passed said user definable criteria for retention wherein said stored elements are correlative to machine status.
Viewed from a eighth vantage point, it is an object of the present invention to provide a method for compressing measurement data correlative to machine status, the steps including: continuously sensing cyclic machine vibration from at least one machine in the form of electrical signals correlative to machine status; sensing at least one mechanical phase reference mark on a rotating shaft of at least the one machine; relating the mechanical phase reference mark of the rotating shaft to the electrical signals of machine vibration wherein the mechanical angle defines intervals of electrical signals; sampling the machine vibration electrical signals under the orchestration of a control signal; transforming said sampled signals into spectral elements; converting said spectral elements into amplitude and phase elements; comparing both the magnitude and phase of each subsequent interval of elements with a previous interval of elements to determine if the amplitude and/or phase of each subsequent element has changed more than a user definable amount from the element of a previous interval; communicating the changed element values to a remote site for storage.
Viewed from a ninth vantage point, it is an object of the present invention to provide a device for compressing measurement data correlative to machine status, said device comprising in combination: at least one sensor operatively coupled to a machine for sensing data correlative to machine status; sampling means operatively coupled to at least said one sensor for sampling said sensed data into discrete elements; processor means operatively coupled to said sampling means for transforming said discrete elements into spectral elements and converting said spectral elements into magnitude and phase elements; means for defining intervals of magnitude and phase elements; means for storing a current interval of magnitude and phase elements; means for comparing a subsequent interval of magnitude and phase elements with said current interval of magnitude and phase elements; means for storing only said elements from said subsequent interval which are anomalous because they differ by a criteria from comparable elements of said current interval of elements wherein compressed measurement data correlative to machine status is continuously captured.
These and other objects will be made manifest when considering the following detailed specification when taken in conjunction with the appended drawing figures.